[core] Move `helpers` to `@mui/x-internals` package

[LukasTy]

I've noticed that many packages duplicate the same type definitions. Given that we have the @mui/x-internals package, it felt like a better place to colocate them there.

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[alexfauquette]

I created it to have a single interface that can apply default value and add additional props, but 95% of the time we don't add new props and MakeRequired is sufficient.

For charts I checked, and I misunderstood it, such that to add additional props, I do it manually instead of using the 3rd generic 🙈

seriesInput: DefaultizedProps<BarSeriesType, 'id'> & { color: string }

[LukasTy]

I would just rename the endpoint to something more specific than helpers to make clear its type helpers.

Does types sound good enough? We could also go for helper-types if we want the specificity, but I'm not sure we need it in this case. 🤔

[flaviendelangle]

For charts I checked, and I misunderstood it, such that to add additional props, I do it manually instead of using the 3rd generic 🙈

I also forgot at some point, that's why I think I did a bad abstraction in the first place :laughing:

[flaviendelangle]

Does types sound good enough?

In the pickers and the tree view we use models for the endpoint with only types/interfaces. But as you want, we can change in the future if needs be, both types and helper-types are more explicit than helpers.

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[LukasTy]

In the pickers and the tree view we use models for the endpoint with only types/interfaces. But as you want, we can change in the future if needs be, both types and helper-types are more explicit than helpers.

Gotcha. 👍 Yeah, models also make sense for types, but given that these are general types, I would prefer types instead. Especially given this package name. 🙈 🤷 https://github.com/mui/material-ui/tree/master/packages/mui-types

[flaviendelangle]

Yeah, models also make sense for types, but given that these are general types, I would prefer types instead. Especially given this package name. 🙈 🤷

Good for me :+1: